1. Technical Field
The present invention relates to rotors for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators, and to methods of manufacturing the rotors. In addition, the invention can also be applied to industrial machines and household electrical appliances.
2. Description of Related Art
There are known rotors for electric rotating machines which include a rotor core formed by stacking a plurality of magnetic steel sheets and a pair of end plates that are respectively provided on opposite axial end faces of the rotor core so as to together sandwich the rotor core (see, for example, Japanese Patent Application Publication No. H9-233750).
However, with such a laminated structure, the rotor core may spread in the axial direction thereof.
For example, when the electric rotating machine is of an inner rotor type, during high-speed rotation of the rotor, the rotor core may spread in the axial direction at the axial ends thereof on the radially outer side (i.e., on the radial side facing a stator of the electric rotating machine).
There is also known a technique for solving the above problem. Specifically, according to the technique, as shown in FIGS. 20A-20B, for each of the end plates 101 of the rotor 100, the thickness of the end plate 101 is increased at a radially outer end portion (i.e., at a stator-side end portion) thereof by protruding the radially outer end portion axially inward from the other portions of the end plate 101. Consequently, the radially outer end portions of the end plates 101 become able to press the rotor core 102 axially inward, thereby preventing the rotor core 102 from spreading at the axial ends thereof on the radially outer side.
With the above technique, however, each of the end plates 101 is deflected for enabling the radially outer end portion thereof to press the rotor core 102 axially inward. Consequently, stress concentration due to the deflection of the end plate 101 (to be shortly referred to as deflection stress concentration hereinafter) will occur at a radially inner end portion (i.e., a non-stator-side end portion) 103 of the end plate 101.
On the other hand, the radially inner end portions 103 of the end plates 101 abut a rotating shaft 106 of the rotor 100. Consequently, it is easy for concentration of load due to impact or vibration applied to the rotor 100 (to be shortly referred to impact load concentration hereinafter) to occur at the radially inner end portions 103 of the end plates 101.
That is, in the rotor 100 shown in FIGS. 20A-20B, both deflection stress concentration and impact load concentration occur at the same spots (i.e., the radially inner end portions 103) of the end plates 101.
As a result, it may be difficult to secure high durability and high impact resistance (or shock resistance) of the end plates 101.